The human rights NGO Amnesty International has raised the alarm of civilians being killed in Syria’s western Aleppo by armed opposition groups. Having called the attacks on government-controlled areas “unlawful,” the group said that weapons banned by international law had also been used.

“The goal of breaking the siege on eastern Aleppo does not give armed opposition groups a license to flout the rules of international humanitarian law by bombarding civilian neighborhoods in government-held areas without distinction,” Deputy Director of Campaigns at Amnesty International’s Beirut regional office, Samah Hadid, said.

In a statement published on Monday, the organization accused armed opposition groups of “a shocking disregard for civilian lives.” The latest offensive on western Aleppo launched on October 28 saw “indiscriminate attacks on civilian areas,” the group said, adding that dozens of innocent people, including children, were killed in the areas, controlled by the Syrian government.

The organization also accused the armed Syrian opposition of “a war crime,” citing allegations that an attack with the use of “toxic gas” was launched on western Aleppo on Sunday. According to the Syrian state news agency SANA, dozens were injured in the chemical weapons attack.

"We are as well investigating this incident, trying to gather witness testimonials about what happened, but what we saw in the videos is symptoms of some kind of an alleged chemical attack," Amnesty International Syria researcher Diana Semaan told RT.

"We call on all parties of the conflict to adhere to international humanitarian law, and we are documenting these violations with the purpose of calling on these perpetrators to end these attacks. So we've been calling on the Syrian government, non-state armed groups and the US-led coalition to end unlawful attacks on civilians," Semaan said.

The human rights group's call echoes a recent UN statement, in which the international body condemned "relentless and indiscriminate" attacks carried out by opposition groups in the western districts of Aleppo.

Saying that the offensive has caused "scores" of civilian deaths over the past several days, the UN special envoy for Syria, Staffan de Mistura, stated he was "appalled and shocked by the high number of rockets indiscriminately launched by armed opposition groups."

From February to September, "the opposition groups that are supposed to be under the US control" have launched hundreds of violent attacks, resulting in some 12,800 civilian deaths, Russia's Permanent Mission to the UN said in a statement last week.

While Russia negotiated with the Syrian authorities to make the cessation of hostilities possible, Washington failed to deliver on its promise to agree the same with the 'moderate' Syrian opposition, which it largely supports, the UN mission said.

Moscow has been assisting the Syrian Army in fighting Al-Nusra Front terrorists and their accomplices in eastern Aleppo, which has become the jihadists' stronghold in Syria. Yet, following the established humanitarian pause, recently the Russian and Syrian Air Forces have been observing a no-fly-zone over Aleppo and nearby neighborhoods. But terrorists in Aleppo continue to intensively shell residential areas and humanitarian corridors, causing civilian suffering, the Russian Ministry of Defense has said.